Decoupling Structural Stability and Oxygen Mobility in Perovskites via A-Site Cation Engineering

The rational design of perovskite oxygen carriers for chemical looping is fundamentally constrained by the structural stability and high oxygen mobility. Decoupling these properties requires moving beyond compositional tuning to uncover their atomic-scale structural origin. Herein, by employing AMnO₃ (A = Ca, Sr, Ba) as a model system, we directly unveil that the A-site cation orchestrates the connectivity of MnO₆ octahedra, providing a powerful structural descriptor to reveal the intrinsic nature of the material. Atomic-resolution AC-HAADF-STEM imaging provides direct atomic-scale evidence: CaMnO₃ retains a robust, three-dimensional network of corner-shared octahedra, while SrMnO₃ and BaMnO₃ form less stable face-sharing configurations, inducing destabilizing Mn⁴⁺-Mn⁴⁺ electrostatic repulsion. This structural divergence dictates redox reversibility; only corner-shared CaMnO₃ undergoes fully reversible phase transitions during cycling. The corner-sharing structure endows CaMnO₃ with the largest specific free volume (SFV) for fast oxygen transport and an O 2p-band center closest to the Fermi level, a signature of weak Mn-O bonds that enables facile lattice oxygen release and moderate oxygen vacancy formation energy for lattice oxygen with mild activity inhibiting excessive oxidation of ethane. Furthermore, strong Mn-O covalency leads to electron localization upon oxygen vacancy formation, generating (Mn³⁺-V_o^••-Mn³⁺) complexes that function as unified active sites for both O₂ chemisorption and CO₂ activation, evidenced by congruent O₂-TPD and CO₂-TPD profiles. Consequently, CaMnO₃ achieves outstanding and stable ethane oxidative dehydrogenation performance with 85% C₂H₄ selectivity, 46% C₂H₄ yield over 20 redox cycles. This work establishes "corner-sharing for stability" as a central design principle, shifting from conventional activity screening to octahedral connectivity engineering for developing next-generation, high-durability oxygen carriers.